Challenge: Simulate Anchor Account Validation in Rust

Anchor's #[account] constraints validate accounts automatically. Here you'll implement the same checks manually — this is exactly what Anchor generates under the hood.

Your Task

Implement validate_account(account_owner, expected_owner, is_signer, require_signer, is_writable, require_writable) that performs Anchor-style validation:

1. Check if account_owner == expected_owner → if not, return Err("IncorrectProgramId")
2. Check if signer is required but missing → return Err("MissingRequiredSignature")
3. Check if writable is required but missing → return Err("AccountNotWritable")
4. If all pass, return Ok("Valid")

This mirrors these Anchor constraints:

• #[account(owner = expected_owner)] → ownership check
• Signer<'info> → signer check
• #[account(mut)] → writable check

Check order matters — validate in the order listed above (owner → signer → writable).